Few-layer Ti3C2T MXene delaminated via flash freezing for high-rate electrochemical capacitive energy storage

Few-layer Ti3C2Tx MXene is synthesized from multi-layered Ti3C2Tx via a flash freezing-assisted delamination process. During the flash freezing process, the water molecules in the interlayers of multi-layered MXene are induced to rearrange and produce volume expansion, thus notably expand the MXenes’ interlayer distance to form few-layer MXene. The synthesized few-layer Ti3C2Tx MXene nanosheets display a very small thickness (less than 5 Ti3C2 atom-layers) and expanded interlayer spacing. Consequently, the few-layer Ti3C2Tx exhibits enhanced capacitance (255 F g−1 vs. 177 F g−1 for the multi-layered Ti3C2Tx) and significantly optimized rate capability (150 F g−1 at 200 mV s−1 vs. 25 F g−1 for the multi-layered Ti3C2Tx), because redox-active sites in the few-layer MXene are easily accessible to electrolyte ions. Moreover, an asymmetric supercapacitor is constructed using the few-layer Ti3C2Tx negative electrode and an activated carbon fiber positive electrode. The asymmetric supercapacitor presents a high energy density of 17.9 Wh kg−1 and a high power density of 14 kW kg−1, which is inseparable from its wide voltage window of 1.4 V and the good rate performance of the few-layer Ti3C2Tx MXene electrode. Overall, the flash freezing-assist delamination provides an effective and environmental-friendly strategy to synthesize few-layer MXene materials for high-rate electrochemical energy storage.